I. Field
The following description relates generally to communication systems, and more particularly, to a method and apparatus for facilitating acknowledging successful reception of data transmission for multi-access compatibility in a wireless communication system.
II. Background
In order to address the issue of increasing bandwidth requirements that are demanded for wireless communications systems, different schemes are being developed to allow multiple user terminals to communicate with a single access point by sharing the channel resources while achieving high data throughputs. Multiple In, Multiple Out (MIMO) technology represents one such approach that has recently emerged as a popular technique for next generation communication systems. MIMO technology has been adopted in several emerging wireless communications standards such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. IEEE 802.11 denotes a set of Wireless Local Area Network (WLAN) air interface (air link medium) standards developed by the IEEE 802.11 committee for short-range communications (e.g., tens of meters to a few hundred meters).
One main feature offered by wireless systems like ones that conform to the IEEE 802.11 WLAN standard is the acknowledgement of successfully received packets. Packets are also referred to as frames. Successfully received frames are those, for example, that did not collide with other transmissions; were received with a reception power above the receiver sensitivity threshold; and properly decoded at the receiver. In this IEEE 802.11 WLAN system, an acknowledgment (ACK) is sent by the receiver to the transmitter of the PLCP (Physical Layer Convergence Protocol) Protocol Data Unit (PPDU) upon successful reception of the PPDU. The ACK is sent by the receiver of the PPDU after a period referred to as a Short Interframe Space (SIFS) time so that there is enough time to decode the packet, to check if the frame was intended for the decoding station, and to check for the presence of errors by computing a Cyclic Redundancy Check (CRC).
In wireless communication systems, Medium Access Control (MAC) protocols are designed to exploit several dimensions of freedom offered by the air link medium. The most commonly exploited dimensions of freedom are time and frequency. For example, in the IEEE 802.11 MAC protocol, the time dimension of freedom is exploited through the Carrier Sense Multiple Access (CSMA) protocol. The CSMA protocol attempts to ensure that no more than one transmission occurs in a neighborhood of potential high interference. The frequency dimension of freedom can be exploited by using different channels created by assigning different frequency bandwidths to each channel.
Recent developments have led to the space dimension being a viable option using an approach referred to as Spatial Division Multiple Access (SDMA) can be used for improving utilization of the air link medium by scheduling multiple terminals for simultaneous transmission and reception. Data is sent to each of the terminals using one or more spatial streams. Specifically, a transmitter forms spatial streams of transmission (“transmission streams”) to individual receivers. The spatial streams are orthogonal to each other. Such orthogonal spatial streams may be formed because the transmitter has several antennas and the transmit/receive channel consists of several paths. The receivers may also have one or more antennas such as implemented in receivers supporting Single In, Multiple Out (SIMO) or MIMO transmission methodology.
When a transmitting device, such as an access point, has packets to transmit in multiple stop and wait data flows to different receiving stations, such as access terminals, the transmitting device can use any one of several previously identified approaches to transmit data on the downlink. For example, downlink transmissions may utilize any of the TDMA, CDMA or SDMA transmission methodologies using Aggregate PPDU (APPDU) or OFDMA.
On the uplink, it is expected that all the different receiving stations that have received the transmission successfully shall send an ACK frame back to the transmitting device. It is often most efficient to use a multiple access method such as SDMA or OFDMA to schedule the simultaneous transmission of ACK frames. However, due to the configuration of the current ACK methodology, there is no way the original transmitting station, which is now a receiving station receiving the ACK, can distinguish the ACK from one station to another. Conversely, if one of the receiving stations fails to send an ACK, there is no way for the original transmitting station to know, which of the receivers did not acknowledge. This is due to the reason that there is no unique information about the transmitting station in this ACK frame format. Hence with the current frame format, the common way to transmit ACK frames would be to schedule these ACK frames to be transmitted in a time-staggered, serial fashion.
Consequently, it would be desirable to address one or more of the deficiencies described above.